In U.S. Pat. application Ser. No. 167,078, filed Mar. 11, 1988 and in continuation-in-part application Ser. No. 300,097, filed Jan. 19, 1989, there is disclosed a liquid pump used for conveying fish and other delicate commodities from a first to a second location. The pump there disclosed utilizes the "Coanda" or wall attachment effect to deflect primary liquid injected into a main duct which, if not deflected, otherwise could damage the commodities carried in the main duct by the secondary liquid. Such a pump has inherently greater efficiency due, it is believed, to not only the shear or particle collision effect between the primary liquid injected through the Coanda inlet and the secondary liquid carrying the commodities but also due to the suction effect created by the action of the primary liquid on the Coanda surface.
A further disclosure in the above-identified applications is a first segment upstream of the Coanda surface which diverges from its inlet end and which terminates at its outlet end immediately before the point of injection of the primary liquid from the Coanda orifice. The inside diameter of the outlet end of the first segment is larger than the inside diameter of the second segment downstream of and smoothly merging with the Coanda surface. Yet a further disclosure in the above-identified applications is a second segment which converges downstream from the Coanda orifice and, thereafter, diverges from the minimum inside diameter location.
The apparatus there disclosed, while found useful in some applications, was found unsatisfactory in other respects. Primarily, it was found that fish damage could occur as set out in greater detail hereafter and that the pumping efficiency of the pump was unnecessarily impaired.
The applicant believes the following explanations for the unsatisfactory operation of the liquid pump referred to above are correct. However, such explanations are given in the interests of full disclosure and subsequent events may result in different or amended explanations. Applicant, therefore, would not wish to be bound by the present explanations if they are found to be incorrect or not applicable in the future.
In prior apparatus as disclosed in the aforementioned applications, the first segment diverged smoothly from its inlet end to the outlet end located adjacent the primary liquid injection point through the orifice. The Coanda surface converged to a first inside diameter which was located downstream from the first segment. The inside diameter downstream from the first segment was smaller than the inside diameter of the outlet end of the first segment. For that reason, fishes travelling from the first segment would impact with the converging Coanda surface, thereby causing fish damage or fish kill.
A further problem in the aforementioned applications was in the area of the Coanda orifice where there is a low pressure or "suction" zone created by the primary liquid injection which impairs momentum to the secondary liquid flow and which results in an inherent improvement in efficiency over previous injection type pumps. However, since the first segment diverged, at the point of primary fluid injection there was a reduced velocity in the first segment due to the increased cross section. This reduced velocity and increased area allowed the secondary fluid to be pulled through the second segment by the Coanda effect around the perimeter of the second segment only and an undesirable no flow or reverse flow condition was allowed to exist in the center or core of the second segment. Under some conditions, the core effect would extend into the inlet end of the first section. When such core effect took place, the no flow or reverse flow core would be able to reverse and re-enter the second segment around the perimeter of the second segment due to the Coanda effect. This would satisfy the low pressure area created by the primary fluid injection over the Coanda surface. The result of allowing this core effect to take place was, therefore, a loss of secondary fluid flow and unacceptable turbulence in the area of primary injection.
Yet a further problem with the prior pump was created by the divergence of the second segment from the minimum throat diameter at the Coanda surface to the downstream end of the second segment. This divergence created a larger cross section in the second segment downstream of the Coanda surface and would not permit the effective transfer of the primary fluid momentum throughout the entire cross section of the second segment. This allowed a core of unaffected secondary fluid to exist in the center of the second segment and, under extreme conditions, to extend upstream into the first segment. Such a core resulted in unnecessary turbulence and loss of efficiency.
Yet a further problem with the prior pump related to the width of the Coanda orifice through which the primary liquid flowed. It was determined that if the width of the orifice was too narrow, not enough momentum would be transferred to the secondary liquid because the injected liquid would dissipate too easily into the secondary flow. This resulted in the backpressure allowing a core effect to occur. The core effect was water in the central core of the second segment which, literally, had little or no movement or had even reverse movement thus preventing the pumping and movement of fish.
Yet a further problem with the previous pump related to the liquid injection through the Coanda orifice from the plenum which contained the primary liquid used for injection through the orifice. As the distance from the bottom of the pump increased, the primary liquid would not flow directly radially inwardly after leaving the peripheral injection orifice but, rather, would curve downwardly when viewed from the end. This decreased the Coanda effect and, hence, the efficiency of the pump.